1. Field of the Invention
The present invention relates to spectroscopic analysis Of gas compositions in scaled containers. More specifically, the invention relates to a non-invasive method for selectively analysing gas-mixtures enclosed in a spacing betwee two glass sheets, such as between the panels of a window glazing unit. The present invention also concerns a modular, portable apparatus for analyzing the performace of gas-filled window glazing units.
2. Description of Related Art
Filling gases with low thermal conductivity, e.g. argon, krypton and xenon, as well as low emissivity coatings are used for a considerable reduction of heat transfer in window glazing units. The performance of the glazing units dranatically depends on the gas present in the spacing. For example, xenon and kryton provide mucb better insulation than argon. Also, as the rim seal is not perfectly leak tight, part of the filling gas can diffuse out and air can diffise into the spacing, resulting in dersing insulation performance. In order to predict the storage and opeuting lifetirnes, there is a need for precise analysis of the gas rnixture composition during manufacturing, storage and use. When the window fillings of existing constructions are to be tested, the movability of the measuring unit is of great importance.
Known gas analyzers employing mass-spectrometry and gas-chromatography are not suitable because they require physical contact with analyzed gas volume. Methods based on infrared and Raman spectroscopy are not applicable in the case of noble gas atoms because they essentially probe vibrational frequencies of molecules. Laser spectroscopic methods are not suitable because of complicated and expensive equipment employed. Direct measurements of the absorption spectra are also impossible to utilize in movable devices because the absorption lines of the noble gases occupy the vacuum ultraviolet spectral region not transmitted by the window glazing panels.
There are a number of known methods for spectroscopically analyzing the performance of gas-filled electronic lamps. In particular, a method utilizing optogalvanic phenomenon (U.S. Pat. No. 4,939,926) has been suggested for determining the performance of sealed rf discharged lamps at low pressure. The known method cannot be directly utilized for atmospheric pressure windows. In an embodiment described in the patent, a broad band ultraviolet-visible source is employed, which prevents the use of the method for selective measurements. In order for the optogalvanic approach to provide selectivity, a high-intensity tunable laser source should be used, which prevents the method from coming to portable realization.
DE Published Patent Application No. 195 05 104 discloses a method and an arnangement for testing the purity and pressure of gases for elctrical lamps. For the measurements both pressure dependent and independent emission lines are obtained. The prior art technology is designed for detection of impurities in electronic lamps, especially in those filled with noble gases. An external hf-excitation source with one electrode is used, and the lamp electrode acts as the other electrode. As regards the discharge excitation, the device is not suitable fbr atmospheric-pressure sealed containers because the measuremnet of argon pressure is insensitive when the pressure exceeds 10 kPa. Discharge in extensive volume requires high power of the source which means that portable realization is problematic
A non-invasive pressure enasuring device described in US Pat. No 5,115,668 is used for estimating the luminance of an externally induced, high-frequency glow discharge of a gas in a lamp. Comparison of the measured luminance with calibrated luminance vs. pressure data provides the pressure for the gas. The device employs aan indirect method for pressure dependence of the luminance without any normalizing procedure, which makes it sensitive to geometrical re-arrangement so that the device is not really transportable. The method uses stable rf excitation and applies to a narrow field of application, i.e, low-pressure lamps, and it cannot be applied to atmospheric pressure sealed containers. The device measures the light in integral without wavelength analysis which means that it is not selective to different elements.
U.S. Pat. No. 5,570,179 discloses a measuring sensor and a measuring arrangement for use in the analysis of gas mixture, consisting of a chamber with transparent window(s) and arranged gas flow, two electrodes on the opposite side of the chamber to apply high alternating voltage to the gas flow, and light detector(s) to measure the intensity of radiation emitted through the chamber window in some selected spectral region. The device is designed mainly for surgical use in hospitals. The method is not non-invasive so that it is not applicable for sealed containers like gas-filled window glazing units. The use of two electrodes is impossible in a window units possessing an inner conducting layer.
There are a number of methods and devices specially created for estimating the performance of window glazing units. A known chemical gas monitor for detecting a leak of the window panel (cf. U.S. Pat. No. 4,848,138) uses chemicals, which are reactive with the constituents of air but not reactive with noble gases. The method requires special reconstruction of the window because the virtual chemical must be inserted during window manufacturing, and it cannot be used for existing constructions.
A known non-destructive method for determination of the rare-gas content of higly insulating glazing units (DE Published Patent Application No. 195 21 568.0) allows for the determination of the leak of air into the window spacing, at least, for krypton and xenon. The determination of the relative amount of the noble gas is based upon measuring the sound velocity in the gas filling. The method is, however, mainly applicable to stationary measurements because it requires precise control of measurement condition (tenperature, spacing distantce, etc.), which makes any portable realization very questionable and field measurements impossible. Also, the method is inselective to argon filling, which is the most important in the area. The method is inselective to different noble gases so that it is unable to distinguish, for example, a mixture of krypton with air from proper filling with argon.
To complete the survey of related art, a method of determining the percentage gas content of an insulating glass window unit is known from U.S. Pat. No. 5,198,773. The prior method is based on applying a voltage to opposite panes of the unit, progressively increasing the voltage, monitoring the voltage, recording the value of threshold discharge voltage, and converting the magnitude to perentage gas content between the panes. The method is directed to recognizing the percentage content of some given gas (e.g. argon or sulfur hexafluoride) between gas panel, and it is impossible to apply it for a window unit of unknown filling. In other words, the prior method is not selective to different noble gas fillings. Also, the necessary use of two electrodes prevents the method from measuring units with conducting inner layers, which are commonly used now to improve insulation performance of the production.
It is an object of this invention to eliminate the problems relating to the pior art and to provide a novel method for selectivc identification of gas components present in a gas or gas mixture.
It is another object of the invention to provide a compact, easily movable and inexpensive device, which is suitable for selective identification of gas components typical for insulation window glazing units, i.e., argon, krypton, xenon and air.
These and other objects, together with the advantages thereof over known processes, which shall become apparent fiom specification which follows, are accomplished by the invention as hereinafter described and claimed.
The present invention is based on the concept of discharging the spacing between the panels of the window glazing unit by applying rapidly alternating electrical field to the spacing between the panels of the window glazing unit. To achieve a discharge, a grounded counter-eclectrode is used. In particular, the present invention comprises creating a local excitation of the gas in a glazing unit by using an electrode, while the inner conducting layer of the glaizng unit may serve as the counter-electrode. The emitted light of the discharge is collected from a collection area larger than the emission area, analyzed in different spectral intcrvals and the concentration of a gas of interest is calculated by comparing the intensity of a spectral interval corresponding to said gas with the intensity of another interval.
The localization of the discharge in the vicinity of the end of an electrode having a small end (e.g. a needle-like electrode) allows for collection of the emitted light without routine adjustment of the optical system.
According to the present invention, the apparatus for non-invasive analysis of, e.g., gas-filled window glazing units comprises means for locally applying the rapidly alternating high voltage to the spacing of the window glazing unit to achieve local emission and means for collecting and transporting emitted light. Further, there are means for determining the intensity of at least two different spectral intervals, at least one of which corresponds to the gas component of interest, and means for calculating the ratio between the intensities of the different spectral intervals.
More speciffically, the non-invasive method according to invention is mainly charaterized by what is stated in the characterizing parts of claims 1 and 10.
The apparatus according to the invention is characterized by what is stated in the chargacterizing part of claim 11.
Considerable advantages are achieved by the invention. Thus, factory-adjust lenses can be used to collect the light from the discharge, and the collected light can be transported to light detectors by using fiber optics, which eliminates influence of instability of the discharge geometry.
According to a preferred embodiment, a maodular apparatus is provided, in which the elcetrode used for local application of rapidly alternating high voltage to the spacing of the window glazing unit and the lens or mirror used for collecting the emitted light are arranged in one portable unit (remote sensor unit) which easily can be tratsported to the vicinity of the glazing unit which is to be tested. The remaining part of the apparatus can be mounted into a, likewise movable, separate processing unit. If desired, the remote sensor unit can further be provided with means for displaying the obtained information about the performace of the window glazing unit, so as to provide the person testing the window to obtain the necessary data for evaluating the performance of the window. An additional light detector can also be fined in the remote sensor unit and connected to the processing means with an additional electrical line, a high alternating voltage being automatically applied to a sample container in absence of a discharge through the window glazing unit.
The movability of the device means that it is possible to use it in field to analyze gas components inside window units installed in real buildings, not only during the manufacturing of window glazing units. The selectivity of the device to the gas components means that it distinguishes between the components without information about the gas filling obtained a priori. The device probes the gas components at normal atmospheric pressure. In order to estimate the operation quality of the window units, the device is capable of recognzing a window unit with more than a specified concentration (e.g. 10%) of air in addition to a filed noble gas. For determining the performance of the window unit, the device is further capable of discriminating between different possible noble gases (argon, krypton, xenon). In other words, the device is capable of analyzing the gas composition whlen the gases are argon, krypton, xenon, and air.